Self-aligned, integrated circuit contact

ABSTRACT

Embodiments concern contacts for use in integrated circuits, which have a reduced likelihood of shorting to unrelated portions of an overlying conductive layer due to contact misalignment. Embodiments for forming the integrated circuit include performing a first etching process to pattern the conductive layer, where the etching compound used in the first etching process is relatively selective to the conductive layer&#39;s materials. Embodiments also include performing a second, contact related etching process that removes a portion of any misaligned contacts that were exposed by the first etching process, where the etching compound used in the second etching process is selective to the contacts&#39; materials. The embodiments can be used to form vias and other interconnect structures as well. The modified contacts and vias are adapted for use in conjunction with memory cells and apparatus incorporating such memory cells, as well as other integrated circuits.

This application is a Divisional of U.S. application Ser. No.10/232,214, filed Aug. 29, 2002, now U.S. Pat. No. 6,780,762, which isincorporated herein by reference.

TECHNICAL FIELD

The present invention relates generally to fabrication of conductivestructures on an integrated circuit, and more specifically tofabrication of contacts that are self-aligned to reduce the possibilityof shorting between unrelated portions of an overlying conductive layer.

BACKGROUND

The integrated circuit industry continues to progress in electroniccircuit densification and miniaturization. This progress has resulted inincreasingly compact and efficient semiconductor devices, which in turnenable the systems into which these devices are incorporated to be madesmaller and less power consumptive.

Integrated circuits are fabricated with devices that have microscopicfeatures that can only be manufactured with processing steps thatrequire careful equipment alignment and timing. The manufacturing costsof integrated circuits are expensive because: (1) the processing stepsmust be accomplished with costly and sophisticated equipment andexperienced operators; and (2) such steps are not always successful. Forexample, if the processing equipment, such as a mask, is inadvertentlymisaligned, then the integrated circuit may be fabricated incorrectlyand fail. As a result, processing yields decrease and production costsincrease. Therefore, to reduce manufacturing costs, a fabricationprocess that has enhanced process margins is desirable. Such a processwould permit successful fabrication of integrated circuits, despiteminor misalignments.

A typical integrated circuit includes a semiconductive substrate, uponwhich active and passive devices are formed. These devices areencapsulated in insulating material, and patterned conductive layers areformed over the insulating material to carry signals to the devices.Conductive contacts are used to electrically connect the devices withthe overlying conductive layers. These contacts extend verticallydownward through the insulating material to connect the conductivelayers with doped regions on the substrate or with portions of thedevices. Accordingly, these contacts are often referred to as “contactsto silicon” or “contacts to substrate.” The patterned conductive layers,in turn, can be connected to other conductive layers through vias orother conductive structures.

During fabrication, the active and passive devices are first formed onthe semiconductor substrate, and are encapsulated by the insulatingmaterial. Openings are then formed in the insulating material, andconductive contact material (e.g., tungsten or doped polysilicon) isdeposited in these openings to form the contacts. An etching procedureis then commonly performed to remove unwanted contact material from thetop surface of the insulating material.

A conductive layer of a different material (e.g., aluminum) is thenformed over the insulating material and contacts. The conductive layeris then patterned and etched, using an etching process that selectivelyetches the material of the conductive layer. The result is a conductivelayer with traces overlying and connecting with the top surfaces of thecontacts.

Portions of the conductive layers or structures (e.g., contacts) thatare supposed to be electrically connected are referred to as “relatedmetals.” This is distinguishable from “unrelated metals,” which refersto portions of the conductive layers or structures that are supposed tobe electrically isolated from each other. Unrelated metals typicallycarry independent signals.

Because the contacts and conductive traces are formed during differentprocessing steps, it is necessary to tightly control thephotolithography and etching processes so that each contact sufficientlyconnects with its corresponding, related metal portion within thepatterned conductive layer. For example, the photomask used during thephotolithography process must be precisely aligned, the timing of theduration of the etching process must be accurate, and the steppers mustbe tightly controlled. If these or other sub-processes are notsufficiently accurate, then one or more contacts may provide a shortbetween unrelated metals within the overlying conductive layer, causingdevice failure or performance degradation.

FIG. 1 illustrates a side, cross-sectional view of a portion of asemiconductor wafer after a successful etch of an overlying conductivelayer, where a contact 102 accurately connects with a related, firstmetal portion 104 of the conductive layer. The conductive layer includesfirst metal portion 104 and second metal portion 106. Metal portions 104and 106 are adjacent to each other within the same patterned layer, andare electrically isolated from each other by insulating material 108.For the purposes of this description, metal portions 104 and 106 areunrelated metals.

When accurately aligned, the top surface of contact 102 is connectedwith the first metal portion 104. The contact 102 also is formed in aninsulating material 110, and thus is electrically isolated from thesecond metal portion 106. The likelihood that contact 102 will short tothe second metal portion 106 is dependent on the distance 112 throughthe insulating material 110 between the contact 102 and the second metalportion 106. Because the distance 112 between the contact 102 and thesecond metal portion 106 is relatively long in terms of the processingtechnology de jure, in the example illustrated in FIG. 1, a lowlikelihood exists that a short will develop across contact 102 tounrelated metal portion 106.

FIG. 2 illustrates a side, cross-sectional view of a portion of asemiconductor wafer after unsuccessful processing of an overlyingconductive layer, where first metal portion 204 of the conductive layeris inaccurately aligned with a related contact 202. As with the exampleillustrated in FIG. 1, first metal portion 204 and second metal portion206 are unrelated metals. Because the distance 212 between the contact202 and second metal portion 206 is relatively short, a much higherlikelihood exists that a short will develop across contact 202 to theunrelated metal 206. This may result in device failure or possiblyimpact device performance negatively.

As device sizes continue to decrease, the margin of error in alignmentand etching process timing also decreases, making it more difficult toaccurately align the metal portions in the overlying conductive layerswith their corresponding contacts. As explained above, thephotolithography and etching processes for patterning the conductivelayers must be tightly controlled, and as immune as possible to processvariations that may negatively affect the accuracy of these processes.For example, in a robust process having sufficient process margin, theaccuracy of the photolithography and etching processes should not beaffected by normal process variations. Such variations could include,for example, ambient conditions, vibration, which particular stepper oretcher is used, whether or not the fabrication chamber had been cleanedor otherwise disturbed, who the operator was who entered the processingparameters into the computer, or other process noise that inherentlyoccurs minute-to-minute, day-to-day.

Accordingly, what are needed are processes that are more robust, whichwill result in higher manufacturing yields and will enable device sizesto continue to be decreased. In particular, what are needed areprocesses that are more tolerant of misalignments that might occur whilemasking and etching an integrated circuit's conductive layers, thusreducing the incidence of shorting between these unrelated metalportions. Also needed is an interconnect structure (e.g., a contact)that accurately self-aligns with its corresponding, related metalportion.

SUMMARY

Embodiments of the present invention provide a self-aligned interconnectstructure (e.g., a contact) and a method for fabricating theself-aligned interconnect structure on an integrated circuit, such as adynamic random access memory (DRAM).

For one embodiment, the invention provides a method for forming avertical interconnect structure. The method includes forming a verticalinterconnect structure within an insulating material, where the verticalinterconnect structure is formed from one or more first conductivematerials, and a top surface of the vertical interconnect structure isexposed at a top surface of the insulating material. The method furtherincludes forming a conductive layer above the insulating material, wherethe conductive layer is formed from one or more second conductivematerials that are different from the first conductive materials, andthe conductive layer physically connects with the top surface of thevertical interconnect structure. A first etching process that isrelatively selective to the second conductive materials is thenperformed to pattern the conductive layer, where the first etchingprocess results in an opening that exposes a portion of the top surfaceof the insulating material. A second etching process that is relativelyselective to the first conductive materials is also performed, so thatany portion of the vertical interconnect structure that is exposedwithin the opening is removed, resulting in a modified verticalinterconnect structure.

For another embodiment, the method includes forming a portion of thesemiconductor device, which includes a layer of insulating material thatdefines a top surface of the portion of the semiconductor device, andforming a contact opening extending vertically downward from the topsurface to an underlying area of the semiconductor device. The methodfurther includes depositing one or more first conductive materials intothe contact opening to form a contact to the underlying area, where atop surface of the contact is exposed at the top surface of theinsulating material. The method also includes forming a conductive layerabove the insulating material, where the conductive layer is formed fromone or more second conductive materials that are different from thefirst conductive materials, and the conductive layer physically connectswith the top surface of the contact. Additionally, the method includesperforming a first etching process that is relatively selective to thesecond conductive materials to pattern the conductive layer, where thefirst etching process results in an opening that exposes a portion ofthe top surface of the insulating material, and performing a secondetching process that is relatively selective to the first conductivematerials, so that any portion of the contact that is exposed within theopening is removed, resulting in a modified contact structure.

For yet another embodiment, the method includes forming a portion of asemiconductor device, which includes a layer of insulating material thatdefines a top surface of the portion of the semiconductor device, andforming a contact opening extending vertically downward from the topsurface to an underlying area of the semiconductor device. The methodfurther includes depositing one or more first conductive materials,which include tungsten, into the contact opening to form a contact tothe underlying area, where a top surface of the contact is exposed atthe top surface of the insulating material, and forming a conductivelayer above the insulating material, where the conductive layer isformed from one or more second conductive materials, and the secondconductive materials are different from the first conductive materials,and the conductive layer physically connects with the top surface of thecontact. Additionally, the method includes performing a first etchingprocess that is relatively selective to the second conductive materialsto pattern the conductive layer, where the first etching process resultsin a conductive layer opening that exposes a portion of the top surfaceof the insulating material, and performing a second etching process thatreadily etches tungsten, so that any portion of the contact that isexposed within the conductive layer opening is removed, resulting in amodified contact structure. The method also includes depositing aninsulating layer over the conductive layer, which fills the conductivelayer opening and a depression formed during the second etching process.

For a further embodiment, the method includes depositing one or morefirst conductive materials within a contact opening in an insulatingmaterial, where a top surface of the first conductive materials isexposed at a top surface of the insulating material, and forming aconductive layer above the insulating material, where the conductivelayer is formed from one or more second conductive materials that aredifferent from the first conductive materials, and the conductive layerphysically connects with the top surface of the first conductivematerials. The method further includes patterning the conductive layer,which results in an opening that exposes a portion of the top surface ofthe first conductive materials, and forming a modified contact from thefirst conductive materials, where the modified contact has a horizontaltop surface, a vertical side surface, and a notch defined by anon-horizontal and non-vertical surface extending between the horizontaltop surface and the vertical side surface, where below the notch, ahorizontal cross-sectional area of the contact is roughly circular, andabove the notch, the horizontal cross-sectional area of the contact isroughly circular with one edge that is defined by a line that bisectsthe horizontal cross-sectional area.

Further embodiments of the invention include semiconductor structuresproduced using one or more methods of the invention, as well asapparatus, devices, modules and systems making use of such semiconductorstructures.

Because they are more tolerant of misalignment, embodiments of thepresent invention enhance the yield of current integrated circuitdesigns. Also, embodiments of the present invention permit higher devicedensity in future integrated circuit designs. Further features andadvantages of the present invention, as well as the structure andoperation of various embodiments, are described in detail below withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a side, cross-sectional view of a portion of asemiconductor wafer after a successful etch of an overlying conductivelayer, where a contact accurately connects with a first metal portion ofthe conductive layer.

FIG. 2 illustrates a side, cross-sectional view of a portion of asemiconductor wafer after unsuccessful processing of an overlyingconductive layer, where a first metal portion of the conductive layer isinaccurately aligned with a contact.

FIG. 3 illustrates a side, cross-sectional view of portion of asemiconductor device in accordance with an embodiment of the presentinvention.

FIGS. 4-6 are side, cross-sectional views of a portion of asemiconductor device during various processing stages in accordance withan embodiment of the invention.

FIGS. 7-8 are side, cross-sectional views of an enlarged portion of thesemiconductor device of FIG. 6, showing an enlarged view of a contactand an overlying conductive layer during various processing stages inaccordance with an embodiment of the invention.

FIG. 9 is a top-down, cross-sectional view of a contact below an etchednotch in accordance with an embodiment of the invention.

FIG. 10 is a top-down, cross-sectional view of a contact above an etchednotch in accordance with an embodiment of the invention.

FIG. 11 is a top-down, elevational view of portions of a conductivelayer and an underlying contact that has been exposed and etched inaccordance with an embodiment of the invention.

FIG. 12 is another side, cross-sectional view of an enlarged portion ofthe semiconductor device of FIG. 6, showing an enlarged view of acontact and an overlying conductive layer in accordance with anembodiment of the invention.

FIG. 13 is a side, cross-sectional view of a portion of a semiconductordevice with a modified contact in accordance with an embodiment of theinvention.

FIG. 14 is a simplified block diagram of an integrated circuit memorydevice in accordance with an embodiment of the invention.

FIG. 15 is a top-down, elevation view of a wafer containingsemiconductor dies in accordance with an embodiment of the invention.

FIG. 16 is a simplified block diagram of an exemplary circuit module inaccordance with an embodiment of the invention.

FIG. 17 is a simplified block diagram of an exemplary memory module inaccordance with an embodiment of the invention.

FIG. 18 is a simplified block diagram of an exemplary electronic systemin accordance with an embodiment of the invention.

FIG. 19 is a simplified block diagram of an exemplary memory system inaccordance with an embodiment of the invention.

FIG. 20 is a simplified block diagram of an exemplary computer system inaccordance with an embodiment of the invention.

DESCRIPTION OF THE EMBODIMENTS

In the following detailed description of the preferred embodiments,reference is made to the accompanying drawings which form a part hereof,and in which is shown by way of illustration specific embodiments inwhich the inventions may be practiced. These embodiments are describedin sufficient detail to enable those skilled in the art to practice theinvention, and it is to be understood that other embodiments may beutilized and that process or mechanical changes may be made withoutdeparting from the scope of the present invention. It will be recognizedthat the methods of the various embodiments can be combined in practice,either concurrently or in succession. Various permutations andcombinations will be readily apparent to those skilled in the art.

Terminology

The terms “wafer” and “substrate” used in the following descriptioninclude any base semiconductor structure. Both are to be understood asincluding silicon-on-sapphire (SOS) technology, silicon-on-insulator(SOI) technology, thin film transistor (TFT) technology, doped andundoped semiconductors, epitaxial layers of a silicon supported by abase semiconductor, as well as other semiconductor support structuresthat are new or are well known to one skilled in the art. Furthermore,when reference is made to a wafer or substrate in the followingdescription, previous process steps may have been utilized to formregions/junctions in the base semiconductor structure.

The terms “horizontal” and “vertical” are used to explain the relativeorientations of particular views. For the purposes of this description,assuming a semiconductor wafer or device is laid flat along a horizontalplane, a “top-down” or “horizontal” view of the device indicates a viewof the device from above. Conversely, a “side” or “vertical” view of thedevice indicates a view of the device from the side. In the figures, anycut-away view is referred to as a “cross-sectional” view. An“elevational” view is a view of an exterior surface.

The term “contact” used in the following description includes aconductive contact formed between a semiconductor substrate or deviceand an overlying conductive layer. With modifications that would beapparent to those of skill in the art based on the description herein,the embodiments of the invention also can be applied to plugs, vias,trenches, and other vertical interconnect structures. Therefore, theterm “contact” can be construed to include these structures as well. Thefollowing detailed description is, therefore, not to be taken in alimiting sense, and the scope of the present invention is defined onlyby the appended claims.

Self-Aligned Contacts Within Semiconductor Devices

In one embodiment of the present invention, contacts are used aselectrical interconnect structures between a patterned, conductive layerand a semiconductor substrate, plug or device. Using processing methodsdescribed later in accordance with various embodiments, a contactrelated etching process is performed in conjunction with the conductivelayer etch. The contact related etch removes exposed portions of thecontacts that extend toward unrelated metal portions of the overlyingconductive layer.

The contacts of the various embodiments can be formed in submicrondimensions, with a substantial reduction in the likelihood thatmisalignments between the contacts and their related metal portions inthe overlying conductive layer will result in shorts between unrelatedmetal portions in the metal layer. Accordingly, the processes of thevarious embodiments are more robust, enabling increasingly miniaturizeddevices to be fabricated with higher yields and improved performance.

In one embodiment, contacts are used to interconnect portions of anoverlying metal layer with cells of a memory device, such as a DRAM(Dynamic Random Access Memory). A typical DRAM includes an array ofmemory cells. The memory cells are arranged in an array and each cellhas an address identifying its location in the array. The array includesa configuration of intersecting conductive lines, and memory cells areassociated with the intersections of the lines. In order to read from orwrite to a cell, the particular cell in question must be selected oraddressed. The address for the selected cell is represented by inputsignals to a word line decoder and to a digit line decoder. The wordline decoder activates a word line in response to the word line address.The selected word line activates the access gates for each of the memorycells in communication with the selected word line. The digit linedecoder selects a digit line pair in response to the digit line address.For a read operation, the selected word line activates the access gatesfor a given word line address, and data is latched to the digit linepairs.

FIG. 3 illustrates a side, cross-sectional view of a portion of asemiconductor device, which includes a DRAM memory cell. A DRAM cellgenerally consists of a capacitor coupled through a transistor to adigit line. Transistor 318 is activated when a signal is provided todoped node region 324 through a conductive contact 328. When activated,transistor 318 allows data to be stored into or retrieved fromcapacitive structure 332.

The wafer fragment illustrated in FIG. 3 includes a semiconductivematerial 312, field oxide region 314, and wordlines 316, 318. Spacers320 are adjacent wordlines 316, 318. Node locations 322, 324 areadjacent to wordlines 316, 318, and are diffusion regions withinsemiconductive material 312.

Conductive structures 326, 328 extend upward from node locations 322,324 into or through insulating material 330. The upper surface ofconductive structure 326 contacts a capacitor construction 332, whichserves to store a bit of information.

Conductive structure 328 is formed though insulating material 330, andserves as a contact to metal layer 302, which includes the digit line tothe memory cell. During operation, the capacitor construction 332 iselectrically connectable to contact 328 through a transistor gatecomprised by wordline 318. In an alternate embodiment, conductivecontact 328 can make contact with a polysilicon plug (not shown), ratherthan directly contacting node 324.

The intersection of contact 328 and metal layer 302 is indicated inregion 350. Contact 328 connects with a related portion 340 of metallayer 302, and is intended to be electrically isolated from an unrelatedportion 342 of metal layer 302. As will be described in more detaillater, the process for manufacturing the device includes an additionaletching step, after patterning metal layer 302, which serves to increasethe distance between contact 328 and unrelated metal portion 342 ofmetal layer 302, in accordance with an embodiment of the invention.

In one embodiment, some or all digit lines are provided within firstmetal layer 302. The first metal layer 302, in turn, is electricallyconnected to second metal layer 304 through vias 306, which function asvertical interconnect structures through a dielectric layer 308. Thesecond metal layer 304 serves to carry voltage signals that aretransmitted to and received from the first metal layer 302 through vias306. Other dielectric and/or metal layers and vias could exist above thesecond metal layer 304, as well.

It will be understood that the above description of a DRAM cell isintended to provide a general understanding of the memory and is not acomplete description of all the elements and features of a DRAM.Although the description shows how embodiments of the present inventionare implemented in a DRAM, interconnect structures (e.g., contacts 328)fabricated using the embodiments of the invention could be used toprovide electrical interconnections within other types of devices, aswell. For example, the embodiments of the present invention could beimplemented in other types of memory devices, microprocessors,Application Specific Integrated Circuits (ASICs) or virtually any othersemiconductor device having two or more metal layers. In particular, theinvention is equally applicable to any size and type of memory circuitand is not intended to be limited to the DRAM described above. Otheralternative types of devices include SRAM (Static Random Access Memory)or Flash memories. Additionally, the DRAM could be a synchronous DRAMcommonly referred to as SGRAM (Synchronous Graphics Random AccessMemory), SDRAM (Synchronous Dynamic Random Access Memory), SDRAM II, andDDR SDRAM (Double Data Rate SDRAM), as well as Synchlink or RambusDRAMs.

Method of Forming Self-Aligned Contacts

FIGS. 4-6 are side, cross-sectional views of a portion of asemiconductor device during various processing stages in accordance withan embodiment of the invention. For illustration purposes, these figuresdepict the formation of a portion of a DRAM memory device, and a singlememory cell is illustrated.

To begin the process, a portion of a semiconductor device is formed, asillustrated in FIG. 4. In the example embodiment, the portion of thesemiconductor device is a DRAM memory cell, which includes a transistor402 and a capacitive structure 404 formed on a semiconductor substrate406. A detailed description of the processes used to form theillustrated semiconductor device portion is outside the scope of thispatent, and such processes are well known to those of skill in the art.

Basically, forming the illustrated semiconductor device portion involvesforming MOS devices (e.g., transistor 402) and nodes (e.g., node 408) onthe substrate 406 using a sequence of material deposition, doping, andetching processes. Insulating material 412 is then deposited over theMOS devices and nodes. In one embodiment, insulating material 412 isformed from tetraethyloxysilicate (TEOS) and/or borophosphosilicateglass (BPSG), although silicon oxide or other suitable materials couldbe used, as well. Conventionally, the TEOS and BPSG are used to formcapacitors in the DRAM. In addition, the insulating material 412 couldinclude additional dielectric formed on top of the TEOS and BPSG, tocreate a capacitor container and an insulator between contacts (e.g.,contact 410). The additional dielectric could be a nitride, an oxide, ora combination thereof.

In one embodiment, the insulating material 412 is planarized afterdeposition of the BPSG and/or additional dielectric materials, andbefore formation of a contact opening (i.e., an opening in which contact410 will be formed). Preferably, chemical-mechanical polishing (CMP) isused, resulting in a substantially flat topology on the top surface ofthe device. The flat topology permits patterning the contact openingwith lithography equipment having a reduced field of depth. Othermechanical or non-mechanical smoothing techniques may also be used, suchas alternative etch processes (e.g., reactive ion etching) or chemicaldissolution. In another alternate embodiment, these planarizationprocesses are not performed.

A contact opening is then etched through the insulating material 410 toan underlying area of the semiconductor device, using a conventionalphotolithographic and etching procedure. In one embodiment, afterpatterning a photoresist material above insulating material 412, ananisotropic reactive ion etching (RIE) process is used to etch thecontact holes. For example, CHF₃, CF₄ or C₄F₈ could be used as etchants,although other materials could be used, as well. In alternateembodiments, an isotropic etching process could be used.

After the contact opening is etched through the insulating material 410,an adhesive and barrier layer (not shown) are deposited in the contactopening. In one embodiment, deposition of these layers is accomplishedusing chemical vapor deposition (CVD) (e.g., CVD, low pressure CVD(LPCVD), atmospheric pressure CVD (APCVD) or plasma enhanced CVD(PECVD)) procedures. In alternate embodiments, a physical vapordeposition (PVD) process could be used, which is also known assputtering. The adhesive and barrier layer materials can include, forexample, an underlying titanium adhesive layer, at a thickness betweenabout 50 to 500 angstroms, and an overlying titanium nitride barrierlayer, at a thickness between about 100 to 1000 angstroms.

Next the contact material is deposited, completely filling the contacthole and forming contact 410. In one embodiment, the contact material istungsten, which is deposited using a PVD process to a thickness betweenabout 2000 to 8000 angstroms. In other embodiments, the contact materialcould be polysilicon, aluminum, tungsten silicide, tungsten polycide,tungsten hexafluride/silane, titanium silicide or other suitablematerials, and or the contact material could be deposited using CVD(e.g., CVD, LPCVD, APCVD or PECVD) or some other process. Also, thecontact material could be thicker or thinner than the above statedrange. An etching or other material removal procedure (e.g., a chemicalmechanical procedure) is then performed to remove unwanted contactmaterial from the top surface of the insulating material 412, in oneembodiment.

The width or diameter of the contact is in a range of about 0.2-0.35microns, in one embodiment, although the width could be greater than orless than this range, as well. When completed, the contact has ahorizontal, cross-sectional area that is roughly circular, although thecross-sectional area could have other shapes, as well, depending on themask pattern used during the contact opening etch process.

After contact 410 is formed, a top surface of contact 410 is exposed atthe top surface of the insulating material 412, so that the contact 410can subsequently be electrically connected to one or more conductivelayers above the memory cell. Accordingly, contact 410 either extends tothe top of or above insulating material 412, or an opening is formed ininsulating material 412, thus exposing the top portion of contact 410.

After the portion of the semiconductor device is formed, a conductivelayer 502 is deposited above (e.g., on the top surface of) theinsulating material 412 and contact 410, as illustrated in FIG. 5. Thisconductive layer is referred to herein as the first metal layer, or the“M1” layer. The M1 layer 502 comes into physical and electrical contactwith conductive contact 410.

In one embodiment, the M1 layer 502 includes three layers of conductivematerial, which are sequentially deposited using standard depositiontechniques (e.g., CVD, LPCVD, and/or PVD). The lowest layer includestitanium, and has a thickness in a range of about 80-120 angstroms, witha thickness of about 100 angstroms being present in one embodiment. Themiddle layer includes an aluminum/copper alloy, and has a thickness in arange of about 2500-3500 angstroms, with a thickness of about 3000angstroms being present in one embodiment. The top layer includestitanium nitride, and has a thickness in a range of about 200-300angstroms, with a thickness of about 250 angstroms being present in oneembodiment.

In other embodiments, the titanium, aluminum, and titanium nitridelayers could be thicker or thinner than the ranges specified above. Instill other embodiments, the M1 layer 502 could include more or fewerconductive layers (e.g., from 1 to 10), or those layers could be formedfrom different materials (e.g., copper), or those layers could bearranged in a different configuration (e.g., a titanium nitride layercould exist as the bottom layer).

After depositing the conductive material of the M1 layer 502, portionsof the layer are selectively removed, as illustrated in FIG. 6, thusexposing portions of the top surface of the insulating material andportions of any misaligned contacts 410. First, a layer of photoresistmaterial 602 is deposited above the M1 layer 502. The resist layer 602is formed from a material that is light or energy sensitive, such thatresist material receiving exposure will have physical characteristicsdifferent from resist material not receiving exposure. Such resistmaterials are typically reactive to a specific set or range of energytypes (e.g., a specific set or range of wavelengths of light).

In one embodiment, the resist layer 602 is formed from an antireflectioncoating material, which is a dark material that helps in the imaging andpatterning of M1 layer 502. This coating also can slow later etchingprocesses down, in some cases. In one embodiment, the antireflectioncoating is formed from siliconoxynitride. In other embodiments, numerousother photoresist compositions (e.g., titanium nitride) and technologiescould be used.

A reticle or mask is placed over the resist layer 602 in order toselectively block waves directed toward the surface of the resist layer.The resist layer 602 is then exposed to electromagnetic radiation orlight waves, typically UV light, of a type capable of exposing theresist material in the resist layer. In one embodiment, the resist layercontains photoresist material of a positive type (i.e., that which ismore easily removed, or more vulnerable to solvents, when exposed tolight or energy). Exposed resist portions are then removed usingconventional washing techniques (e.g., washing with a solution ofaqueous TMAH), leaving portions of the M1 layer 502 uncovered. In analternate embodiment, a negative type photoresist could be used (i.e.,that which is more resistant to removal, when exposed to light orenergy, than unexposed areas of the resist). In the latter embodiment,the mask or reticle would be appropriately and obviously modified.

After the photoresist is selectively removed, a patterned layer ofresist 602 remains on the top surface of M1 layer 502. Uncoveredportions of M1 layer 502 are then modified and removed, resulting in theformation of M1 opening 604.

In one embodiment, the uncovered portions of the M1 layer 502 areremoved using an anisotropic RIE procedure at a pressure between about 6to 20 mtorr, although other etching procedures and/or pressures outsidethis range could alternatively be used. This involves applying a firstetching compound to the remaining photoresist and the uncovered portionsof the M1 layer 502. The first etching compound selectively etches theconductive material within the M1 layer 502. In one embodiment, thefirst etching compound is a chlorine based etchant, having an etchchemistry comprised of between about 20 to 80% chlorine, and betweenabout 20 to 80% BCl₃. Additive reactants, such as argon, nitrogen, CHF₃,and CH₄, between about 0 to 40%, can also be included in the etchingambient. Numerous other etching materials, such as Cl₂, for example,could be used in other embodiments. The selection of the particularmaterial used depends on the conductive material forming the M1 layer,the speed of the desired etch, the materials at which the etch shouldterminate, and other factors. In various embodiments, anisotropic,isotropic, wet or dry etches, or a combination of these types of etchescould be used.

The use of the described etch chemistry, with an etch rate selectivityallowing a greater removal rate for the M1 layer material than for thecontact materials, allows the end point to easily be established withthe appearance of contact 410. Accordingly, the etching process is timedto terminate about when the top of the contact 410 and the insulatingmaterial 412 is exposed with sufficient over-etch to cover normalproduction variations for M1-to-M1 shorts. This results in the formationof openings, such as opening 604, which separate unrelated portions 606,608 of the M1 layer 502.

In one embodiment, remaining resist portions 602 are then removed usingtechniques well known to those of skill in the art, such as plasmaoxygen ashing and careful wet cleans. In other embodiments, theremaining resist portions remain on the surface of the patterned M1layer 502 or are removed at a later time. For ease of illustration,remaining resist portions are not illustrated in the figures thatfollow.

In some cases, mask misalignments can make spatial tolerances worseduring the M1 layer photolithography process, a portion of the top ofcontact 410 also is exposed. Area 610 of the device of FIG. 6 isenlarged, in FIGS. 7-8 and 12, which are side, cross-sectional viewsshowing an enlarged view of a contact 410 and an overlying conductivelayer 606, 608 during various processing stages in accordance with anembodiment of the invention.

Specifically, FIG. 7 illustrates a side, cross-sectional view of acontact 410 having a first top surface portion 702 that is exposedwithin opening 604 due to a misalignment of the M1 photolithographyprocess. This top surface portion 702 extends toward unrelated portion608 of the M1 layer. Contact 410 also has a second top surface portion704 that underlies related portion 606 of the M1 layer.

As described previously, portion 608 of the M1 layer is unrelated metalto both contact 410 and portion 606 of the M1 layer, for the purposes ofthis description. Accordingly, it is desirable to avoid shorting portion606 to portion 608 across contact 410. The likelihood that a short willdevelop depends primarily on the shortest distance 706 between contact410 and unrelated M1 portion 608 across insulating material. Themagnitude of this distance 706 is a function of the original layout andthe amount of misalignment present in the M1 photolithography process.In addition, small fragments of contact material and notches may reduceor breach the distance between contact 410 and unrelated M1 portion 608.

In accordance with an embodiment of the present invention, a contactrelated etch is performed after the M1 layer etch in order to remove aportion of contact 410 and increase the shortest distance betweencontact 410 and unrelated portion 608 of the M1 layer. FIG. 8illustrates a side, cross-sectional view of the enlarged contact 410 ofFIG. 7, after a portion of the contact 410 has been selectively removedin accordance with an embodiment of the invention.

In one embodiment, this etch is an anisotropic RIE procedure at apressure between about 6 to 20 mtorr, although other etching proceduresand/or pressures outside this range could alternatively be used. Duringthis process, the patterned M1 layer acts as a mask, thus protectingunderlying portions of contact 410 and eliminating the need for aseparate photoresist process. In an alternate embodiment, the resistmaterial used during the M1 layer etch could be retained on the topsurface of the M1 layer at least until the contact related etch iscompleted. In still another alternate embodiment, a new resist layercould be applied, patterned, and selectively removed from the areaswhere the contact related etch is desired.

In order to perform the contact related etch, a second etching compoundthat preferentially etches the contact material is applied withincontact opening 604. The second etching compound selectively etches theconductive material within contact 410, along with any adhesive andbarrier layers (not shown). In one embodiment, the second etchingcompound also selectively etches insulating material 412. In anotherembodiment, the second etching compound does not substantially etchinsulating material 412.

In one embodiment, the second etching compound includes nitrogentrifluoride (NF₃), which readily etches tungsten and other materials.Numerous other etching materials could be used in other embodiments. Forexample, etchants containing a halogen compound, SF₃, SF₆, Cl₂, C₂F₆ orother materials also could be used. The selection of the particularmaterial used depends on the conductive material forming the contact,the speed of the desired etch, and other factors. In variousembodiments, a wet etch, dry etch, or a combination of these types ofetches could be used.

The etching process is timed to terminate after the shortest distance806 between contact 410 and unrelated portion 608 of the M1 layer hasbeen increased sufficient to buy back margin loss due to misalignment.This decreases the likelihood that a short will develop across contact410 between unrelated portions 606, 608 of the M1 layer. In oneembodiment, the process is terminated before a significant amount ofcontact material is removed from the contact surface 804 that physicallyconnects to related portion 606 of the M1 layer, although some of thiscontact material could be removed while still maintaining the electricalintegrity of the device.

In one embodiment, the contact related etching process is terminatedwhen a depression 808 that spans the distance between the unrelatedmetal portions 606, 608 is formed, where the depression 808 has aconcave and roughly half-circular perimeter. Accordingly, the exposedsurface 802 of contact 410 also is concave between its top surface 804and its side surface 810. In other embodiments, the depression 808 couldhave a more triangular perimeter (i.e., the exposed surface 802 ofcontact 410 would be roughly straight between the contact's top surface804 and the side surface 810).

The contact related etching process results in a contact 410 having ahorizontal top surface 804, a vertical side surface 810, and a notchdefined by a non-horizontal and non-vertical surface 802 extendingbetween point 812 on the top surface 804 and point 814 on the verticalside surface 810. Below the notch, the horizontal cross-sectional areaof the contact is roughly circular in one embodiment, as depicted inFIG. 9, which illustrates a top-down, enlarged, cross-sectional view ofthe contact 410 of FIG. 8 when cut through cross-section lines 9-9. Inone embodiment, the diameter 902 of the contact 410 is in a range ofabout 0.2-0.35 microns, although the diameter could be larger or smallerin other embodiments.

Above the notch, the horizontal cross-sectional area of the contact isroughly circular with one straight edge 1002 that is defined by a linethat bisects the circular cross section, in one embodiment, as depictedin FIG. 10, which illustrates a top-down, enlarged, cross-sectional viewof the contact 410 of FIG. 8 when cut through cross-section lines 10-10.In other embodiments, where the contact 410 does not normally have acircular, horizontal cross-sectional area, but has a cross-sectionalarea of another shape instead (e.g., rectangular, square, oval, ormulti-sided), the shapes depicted in FIGS. 9 and 10 would lookaccordingly different.

FIG. 11 is a top-down, elevational view of portions 606, 608 of aconductive layer and the surface of a contact 410 that has been exposedand etched in accordance with an embodiment of the invention. Whenviewed from the top, a part 1102 of the surface of contact 410 isexposed. Another part 1104 of the surface of contact 410 is underneathand hidden by related portion 606 of the M1 layer, as indicated bydashed lines. In one embodiment, after the contact related etch iscompleted, both the exposed part 1102 of the contact and exposedportions of the dielectric 412 within which the contact 410 is locatedare partially removed, forming a depression (see depression 808, FIG. 8)between portions 606 and 608 of the M1 layer.

In the above described sequence of processes, the M1 etch and thecontact related etch are performed sequentially as separate processes,where the first etching compound used in the M1 etch is selective to theM1 layer materials, but is not selective to the contact material, andwhere the second etching compound is not selective to the M1 layermaterials but is selective to the contact material. In anotherembodiment, the first and second etching compounds are combinedtogether, so that the M1 layer etch and the contact related etch occurwithin the same processing step.

After completing the contact related etch, an interlayer dielectric(ILD) material is deposited above the M1 layer 606, 608 and into thecontact opening, thus filling the depression (e.g., depression 808, FIG.8) between unrelated M1 layer portions 606, 608. FIG. 12 illustrates aside, cross-sectional view of the device portion of FIG. 8, after ILDmaterial 1202 has been deposited over the M1 layer 606, 608 and into thecontact opening. Deposition of ILD 1202 is performed in a manner knownto persons skilled in the art.

In one embodiment, ILD 1202 is formed from tetraethyloxysilicate (TEOS).ILD 1202 has a thickness in a range of about 4500-5500 angstroms, with athickness of about 5000 angstroms being present in one embodiment. Inother embodiments, ILD 1202 could be formed from other suitabledielectric materials, and could be thicker or thinner than the rangespecified above. For example, ILD 1202 could include other insulatingmaterials, such as oxides or nitrides.

Subsequent processing steps can then be performed to forminterconnections with the M1 layer and to complete the integratedcircuit. FIG. 13 is a side, cross-sectional view of a portion of asemiconductor device with a modified contact 1302 in accordance with anembodiment of the invention. Specifically, the portion of thesemiconductor device is a DRAM memory cell, although contacts orinterconnects formed using the embodiments of the present inventioncould be implemented in other types of memory cells or devices, as well.

As FIG. 13 illustrates, contact 1302 is modified so that a depression1304 exists between unrelated portions 1306, 1308 of the M1 layer. Thedepression 1304 is filled with ILD material 1310, which also forms adielectric layer above the M1 layer. In one embodiment, after LD 1310has been deposited, it is planarized using a chemical-mechanicalpolishing (CMP) process to smooth the top surface. Smoothing the topsurface of LD 1310 has been shown to improve the overall performance ofthe device. Other mechanical or non-mechanical smoothing techniques mayalso be used, such as alternative etch processes (e.g., RIE) or chemicaldissolution. In another embodiment, the top surface is not planarized.

Conductive vias 1312 are formed through ILD 1310, providinginterconnections between the M1 layer 1306, 1308 and another overlying,patterned conductive layer 1314, sometimes referred to as the M2 layer.The M2 layer 1314 and vias 1312 are formed using techniques andmaterials well known to those of skill in the art. After patterning theM2 layer 1314, one or more additional layers of dielectric andconductive material can be built on top of the M2 layer 1314 (e.g., M3,M4, etc.). In addition, interconnects between the M1, M2, and/or the newconductive layers can be formed. Alternatively, a passivation layer canbe formed on top of the M2 layer 1314, after which the device build-upprocess can be considered to be essentially complete.

The memory cells described above can form a portion of a memory device,in accordance with various embodiments. This memory device can be, forexample, a DRAM, SRAM, Flash memory or other type of memory device.Alternatively, the self-aligned contacts and their formation methods,described in conjunction with the various embodiments above, can beintegrated into another type of device (e.g., a microprocessor or ASIC).

Memory Devices

FIG. 14 is a simplified block diagram of an integrated circuit memorydevice according to one embodiment of the invention. In one embodiment,memory cells, such as those described in conjunction with FIGS. 3 and13, are suitable for use in memory devices. Other types of memory cellshaving structures well understood in the art are also suitable for usein memory devices.

The memory device 1400 includes an array of memory cells 1402, addressdecoder 1404, row access circuitry 1406, column access circuitry 1408,control circuitry 1410, and Input/Output circuit 1412. The memory can becoupled to an external microprocessor 1414, or memory controller formemory accessing. The memory receives control signals from the processor1414, such as WE*, RAS* and CAS* signals. The memory is used to storedata which is accessed via I/O lines. It will be appreciated by thoseskilled in the art that additional circuitry and control signals can beprovided, and that the memory device of FIG. 14 has been simplified tohelp focus on the invention. The memory device is formed usingtechniques described above, in accordance with the various embodimentsof the invention.

As recognized by those skilled in the art, memory devices of the typedescribed herein are generally fabricated as an integrated circuitcontaining a variety of semiconductor devices. The integrated circuit issupported by a substrate. Integrated circuits are typically repeatedmultiple times on each substrate. The substrate is further processed toseparate the integrated circuits into dies as is well known in the art.

Semiconductor Dies

FIG. 15 is a top-down, elevation view of a wafer 1500 containingsemiconductor dies 1510 in accordance with an embodiment of theinvention. A die is an individual pattern, typically rectangular, on asubstrate that contains circuitry, or integrated circuit devices, toperform a specific function. At least one of the integrated circuitdevices includes a modified contact, embodiments of which are disclosedherein. A semiconductor wafer will typically contain a repeated patternof such dies containing the same functionality. Die 1510 may containcircuitry for the inventive memory device, as discussed above. Die 1510may further contain additional circuitry to extend to such complexdevices as a monolithic processor with multiple functionality. Die 1510is typically packaged in a protective casing (not shown) with leadsextending therefrom (not shown) providing access to the circuitry of thedie for unilateral or bilateral communication and control.

Circuit Modules

FIG. 16 is a simplified block diagram of an exemplary circuit module1600 in accordance with an embodiment of the invention. As shown in FIG.16, two or more dies 1510 may be combined, with or without protectivecasing, into circuit module 1600 to enhance or extend the functionalityof an individual die 1510. Circuit module 1600 may be a combination ofdies 1510 representing a variety of functions, or a combination of dies1510 containing the same functionality. Some examples of a circuitmodule include memory modules, device drivers, power modules,communication modems, processor modules, and application-specificmodules and may include multilayer, multichip modules. Circuit module1600 may be a subcomponent of a variety of electronic systems, such as aclock, a television, a cellular or radio communication device (e.g.,cell phone, pager, etc.), a desktop, handheld or portable computer, anautomobile, an industrial control system, an aircraft, an automatedteller machine, and others. Circuit module 1600 will have a variety ofleads 1610 extending therefrom and coupled to the dies 1510 providingunilateral or bilateral communication and control.

FIG. 17 is a simplified block diagram of an exemplary memory module1700, which is one embodiment of a circuit module. Memory module 1700generally depicts a Single Inline Memory Module (SIMM) or Dual InlineMemory Module (DIMM). A SIMM or DIMM is generally a printed circuitboard (PCB) or other support containing a series of memory devices.While a SIMM will have a single in-line set of contacts or leads, a DIMMwill have a set of leads on each side of the support with each setrepresenting separate I/O signals. Memory module 1700 contains multiplememory devices 1710 contained on support 1715, the number depending uponthe desired bus width and the desire for parity. Memory module 1700 maycontain memory devices 1710 on both sides of support 1715. Memory module1700 accepts a command signal from an external controller (not shown) ona command link 1720 and provides for data input and data output on datalinks 1730. The command link 1720 and data links 1730 are connected toleads 1740 extending from the support 1715. Leads 1740 are shown forconceptual purposes and are not limited to the positions shown in FIG.17.

Electronic Systems

FIG. 18 is a simplified block diagram of an exemplary electronic system1800 in accordance with an embodiment of the invention. Electronicsystem 1800 contains one or more circuit modules 1600. Electronic system1800 generally contains a user interface 1810. User interface 1810provides a user of the electronic system 1800 with some form of controlor observation of the results of the electronic system 1800. Someexamples of user interface 1810 include a keyboard, pointing device,monitor, and printer of a computer; a keypad, speaker, microphone, anddisplay of a communication device; a tuning dial, display, and speakersof a radio; an ignition switch and gas pedal of an automobile; and acard reader, keypad, display, and currency dispenser of an automatedteller machine. User interface 1810 may further describe access portsprovided to electronic system 1800. Access ports are used to connect anelectronic system to the more tangible user interface componentspreviously exemplified.

One or more of the circuit modules 1600 may be a processor providingsome form of manipulation, control or direction of inputs from oroutputs to user interface 1810, or of other information eitherpreprogrammed into, or otherwise provided to, electronic system 1800. Aswill be apparent from the lists of examples previously given, electronicsystem 1800 will often contain certain mechanical components (not shown)in addition to circuit modules 1600 and user interface 1810. It will beappreciated that the one or more circuit modules 1600 in electronicsystem 1800 can be replaced by a single integrated circuit. Furthermore,electronic system 1800 may be a subcomponent of a larger electronicsystem.

FIG. 19 is a simplified block diagram of an exemplary memory system1900, which is one embodiment of an electronic system. Memory system1900 contains one or more memory modules 1700 and a memory controller1910. Memory controller 1910 provides and controls a bidirectionalinterface between memory system 1900 and an external system bus 1920.Memory system 1900 accepts a command signal from the external bus 1920and relays it to the one or more memory modules 1700 on a command link1930. Memory system 1900 provides for data input and data output betweenthe one or more memory modules 1700 and external system bus 1920 on datalinks 1940.

FIG. 20 is a simplified block diagram of an exemplary computer system2000, which is a further embodiment of an electronic system. Computersystem 2000 contains a processor 2010 and a memory system 2000 housed ina computer unit 2005. Computer system 2000 is but one example of anelectronic system containing another electronic system (e.g., memorysystem 1900) as a subcomponent. Computer system 2000 optionally containsuser interface components. Depicted in FIG. 20 are a keyboard 2020, apointing device 2030, a monitor 2040, a printer 2050, and a bulk storagedevice 2060. It will be appreciated that other components are oftenassociated with computer system 2000 such as modems, device drivercards, additional storage devices, etc. It will further be appreciatedthat the processor 2010 and memory system 1900 of computer system 2000can be incorporated on a single integrated circuit. Such single packageprocessing units reduce the communication time between the processor andthe memory circuit.

CONCLUSION

When misalignments are present during photolithography processes used toform prior art integrated circuits, these circuits may suffer fromcontact shorts between unrelated portions of a metal layer. Theseshorting problems affect the manufacturing yields, and restrict theability to further miniaturize integrated circuits because ofconstraints that must be placed on the photolithography processes.

Embodiments of the present invention provide a contact structure, whichis formed using a method that removes material that extends towardunrelated metal, thus increasing the distance between a misalignedcontact and the unrelated metal. This decreases the likelihood that ashort across a misaligned contact will develop between unrelatedportions of an overlying conductive layer. Accordingly, the methods ofthe various embodiments result in processes with higher margins, andhigher manufacturing yields.

While the invention has been described and illustrated with respect toforming contacts to a memory cell, it should be apparent that the sameprocessing techniques can be used to form vias and other connectors,that interconnect with other conductive layers. The process used forforming a via is very similar. The difference is well known in the artand consists of the fact that the via, rather than interconnecting asemiconductor structure and a metal layer, typically interconnects twometal layers. In addition, the methods of the various embodiments can beused for other applications besides memory cells. Modifications thatwould be apparent to those of skill in the art could be made to themethods of the various embodiments to apply the methods to otherintegrated circuits, integrated circuit packages, interposers, printedcircuit boards, and other structures that include vertical interconnectstructures that are formed from material that is different from thematerial of an overlying conductive layer.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement that is calculated to achieve the same purpose maybe substituted for the specific embodiments shown. Many adaptations ofthe invention will be apparent to those of ordinary skill in the art.Accordingly, this application is intended to cover any adaptations orvariations of the invention. It is manifestly intended that thisinvention be limited only by the following claims and equivalentsthereof.

1. A semiconductor die comprising; an integrated circuit supported by asubstrate, the integrated circuit having a plurality of integratedcircuit devices, wherein the integrated circuit comprises: an insulatingmaterial forming a top surface of the integrated circuit; a contactwithin a contact opening in the insulating material, the contactincluding: a horizontal top surface; a vertical side surface; and anotch defined by a non-horizontal and non-vertical surface extendingbetween the horizontal top surface and the vertical side surface; aconductive material overlaying the contact and contacting the horizontaltop surface of the contact; and a dielectric material connected to thenon-horizontal and non-vertical surface defining the notch of thecontact.
 2. The semiconductor die of claim 1, wherein below the notch, ahorizontal cross-sectional area of the contact is roughly circular, andabove the notch, the horizontal cross-sectional area of the contactincludes a roughly circular portion and an edge defined by a line thatsubstantially bisects the horizontal cross-sectional area.
 3. Thesemiconductor die of claim 1, wherein the integrated circuit furthercomprises a node region connected to a bottom surface of the contactopposite the horizontal top surface of the contact.
 4. The semiconductordie of claim 3, wherein the node region comprises a doped node.
 5. Thesemiconductor die of claim 3, wherein the contact is configured to passa signal to activate a transistor connected to the node region.
 6. Thesemiconductor die of claim 1, wherein the contact includes tungsten. 7.The semiconductor die of claim 1, wherein the contact includes aluminum.8. A semiconductor die comprising one or more interconnect structures,wherein at least one of the one or more interconnect structurescomprises: an insulation material; a conductive material overlaying theinsulation material; a conductive interconnect disposed in an opening ofthe insulation material and underlying a portion of the conductivematerial, the conductive interconnect comprising: a horizontal topsurface connected to the conductive material; a vertical side surface;and a notch defined by a non-horizontal and non-vertical surfaceextending between the horizontal top surface and the vertical sidesurface; a dielectric material connected to the non-horizontal andnon-vertical surface defining the notch of the conductive interconnect.9. The semiconductor die of claim 8, wherein the conductive interconnectincludes tungsten.
 10. The semiconductor die of claim 8, wherein theconductive interconnect includes aluminum.
 11. The semiconductor die ofclaim 8, wherein below the notch, a horizontal cross-section area of theconductive interconnect is roughly circular.
 12. The semiconductor dieof claim 8, wherein, above the notch, a horizontal cross-section area ofthe conductive interconnect includes a roughly circular portion and oneedge defined by a line that bisects the horizontal cross-section. 13.The semiconductor die of claim 8, wherein the at least one of the one ormore interconnect structures further comprises a node region connectedto the conductive interconnect.
 14. The semiconductor die of claim 13,wherein the node region is connected at a bottom surface of theconductive interconnect opposite the substantially horizontal topsurface.
 15. The semiconductor die of claim 13, wherein the node regioncomprises a doped node.
 16. The semiconductor die of claim 15, whereinthe conductive interconnect is configured to pass a signal to activate atransistor connected to the doped node.